Currently, intravascular catheters are often manufactured by forming a braided tube, typically made of stainless steel fibers or strands, over a mandrel. Often, the actual braiding takes place about an inner tube of polytetrafluoroethylene (PTFE) which, in turn, is carried on the mandrel, with the PTFE tube defining the lumen of the catheter formed by the process.
Then, after formation of the tubular braid, a plastic layer is extruded about the braided material to create the catheter body. Following this, a tubular transitional tip is sealed to one end of the catheter body. Typically, the transition tip is not reinforced with braid as is the rest of the catheter, so that the transition tip is softer and more flexible than the rest of the catheter.
Following this, in some commercial catheter designs, an added flexible tip is bonded to the free end of the tubular transition tip, with the added flexible tip containing a high loading of radiopaque agent.
For example, PTCA guiding catheters sold by The Cordis Corporation may be manufactured in this manner.
To develop large lumen catheters with a given outer diameter, the catheter wall needs to be as thin as possible. However, thin, unreinforced plastic tubing tends to kink easily, particularly where the wall thickness is less than 15 percent of the outer diameter. In order to create a flexible, yet not collapsible tubing as is needed particularly in the transitional tip area, a helical wire reinforcement has been proposed to be added to the transition tip, to provide a tubing which can have a thin wall, and can be flexible, but is resistant to collapse. The remainder of the catheter body may be reinforced with a braided tubular reinforcement. Such a proposal has been made in Castaneda et al. U.S. patent application No. 559,193, filed Jul. 27, 1990, and entitled Intravascular Catheter With Kink Resistant Tip.
In both the commercially available catheters where the tubular transition tip is unreinforced, and in the catheter of the above cited application where a helical wire reinforcement is provided, the tubular transition tip is attached to the main body of the catheter, (which typically contains a tubular, braided reinforcement) by bonding of respective ends together. Accordingly, this bond is extremely critical, since a defective bond can result in accidental separation of the transition tip from the main body of the catheter and loss thereof within a patient.
By this invention, a catheter is provided which has a catheter section such as a transition tip of significantly different physical properties from the main body of the catheter. However, despite this, there is virtually no possibility of separation of the one catheter section from the other, even if a fuse joint between the plastic of the two sections is defective. The catheters of this invention may exhibit softer, more flexible transition tips and harder, stiffer catheter main bodies, to achieve the desired characteristics of a catheter through variable physical properties along the length thereof. Likewise, the catheters of this invention can exhibit transition tips or other sections which are softer and more flexible than the catheter main body without being strongly prone to collapsing or kinking.